1. Field of the Invention
The present invention relates to vibratory bowl finishing machines, and in particular, to an improvement in a reversing weight assembly for a vibratory bowl finishing machine.
2. Problems in the Art
Vibrating finishing machines or vibratory bowl finishing machines are well known in the art. They have been used for many years to deburr or finish manufactured parts.
A general discussion of such machines can be found at U.S. Pat. No. 4,329,817 which in turn cites numerous earlier patents involving vibratory finishing machines of this type. For purposes of this background, U.S. Pat. No. 4,329,817 is incorporated by reference.
It is crucial to an understanding of vibratory bowl finishing machines that the upper and lower eccentric weights control the action of the abrasive medium and parts being finished in the machine. The weights must be eccentric in the sense that the center of gravity of each weight is offset from the longitudinal axis of the drive shaft, but also these eccentric weights should have their center of gravity vertically offset from each other to impart desired vibratory motion in the machine.
Generally the eccentric weights consist of members which extend typically laterally from a line defining the rotational axis of the weights. There is therefore required an angular offset between the radial direction of the top eccentric weight from the rotational axis versus the radial direction of the lower eccentric weight from the rotational axis.
This offset determines both the volatility of action set up in the finishing machine, as well as the speed of movement of the machine and the items in the bowl of the machine. For purposes of this description, these factors will be designated in terms of the aggressiveness and speed produced by the machine.
The vibratory bowl finishing machine can be operated in two modes. The first will be referred to as the work mode where the products to be finished are introduced into the medium, and the machine is operated to cause deburring and finishing of the products. The vibrations generated by the offset eccentric weights contribute to a "scrolling" type motion of the mixture in the bowl; that is, a constantly turning over of that mixture, along with a circular slightly vertical amplitude. By utilizing a bowl, the contents of the bowl can be kept in a continual controlled but churning and circulating motion.
The direction of motion is also determined by the position of offset of the eccentric weights. The bottom weight is referred to as the leading weight. The bottom weight is angularly offset to lead the top weight. Of course, denomination of leading versus trailing depends on the direction of rotation of the drive axle. The bottom eccentric weight should always lead the top weight in the direction of rotation of the drive axle.
It is therefore to be understood that positioning the weights determine at least the aggressiveness of the mixture in the bowl and the speed of the mixture in the bowl, as well as the direction of movement of the mixture in the bowl.
Adjustment of the angular offset of the eccentric weights to change these parameters has been recognized in the prior art, as is discussed in the patent incorporated by reference above. It was further recognized that to facilitate easier separation of the parts from the abrasive media after finishing, methods could be developed to reverse the direction of movement of the mixture in the bowl. One way was to insert a ramp (or what in the art is called a dam) into the bowl and utilize the vibratory motion of the machine to cause the generally heavier finished parts to travel up the dam to an outlet container while keeping the abrasive medium within the bowl.
Output ramps or screens are well known in the art such as are discussed in U.S. Pat. Nos. 4,329,817, and 3,844,071.
It therefore became a need to allow the eccentric weights to be generally reversed in their angular relationships when their direction of rotation is reversed, so that a reversal in direction of movement of the mixture in the bowl could be accomplished. Originally, this was accomplished by simply unfastening at least one of the eccentric weights (usually just one), rotating it to the desired opposite angle, and then tightening it down on the drive shaft again. While fundamentally this was satisfactory for the operation of the machine, it was wasteful of time and resources to require such change upon every reversal of the machine.
Other attempts included using adjustable eccentric weights, which could be more easily fixed into a variety of different angles. This still, however, required the machine to be stopped, the weights changed in angle, and then restarted upon each reversal of the machine.
Recent U.S. Pat. No. 4,452,016, discloses an automatic reversing weight for a vibrating finishing machine. To avoid the manual reorientation of one or more of the eccentric weights on the drive shaft, the top eccentric weight is replaced by a canister having radial dividing baffles at preselected angles. Steel shot of size and weight to cumulatively simulate the weight of an eccentric weight, is positioned inside the canister. When the drive shaft is rotated in one direction, the shot by centrifugal force is thrown to the edge of the canister and against one of the baffles which is positioned so that the shot acts as the eccentric weight at the desired trailing angle from the lower eccentric weight. When reversal is needed, the drive shaft is simply reversed and the steel shot travels by centrifugal force along the inside perimeter of the canister up against the other angled baffle which represents the desired trailing angle for reverse direction for the machine. The U.S. Pat. No. 3,844,071 also reveals an automatically reversing eccentric weight which reverses on detection of changes in motor speed by somewhat similarly transferring the position of weighted balls on the basis of centrifugal force according to direction of rotation of the motor shaft.
The U.S. Pat. No. 3,844,071 also discloses an automatically operating ramp or screen. During the finishing mode of the machine, the screen hingeably rides on top of the mixture in the bowl. However, when direction is reversed, the screen is caused to tilt downwardly to the bottom of the bowl to allow migration of the mixture upwardly.
Although advances have been made in the vibratory bowl finishing machine art, room for improvement still exists. The prior art is deficient in that it still does not allow easy adjustment of the angular offset of the eccentric weights when characteristics of operation of the machine are desired to be changed. As previously stated, change in the offset of the weights will affect aggressiveness and speed of the finishing process. The automatic reversing weight vibratory finishing machines simply do not have an easy, efficient, durable way of adjusting the offset or trailing angle of the top weight.
Furthermore, the current automatic reversing weight machines experience significant wear and tear from the force of the steel shot or weighted balls being thrown in reverse directions by centrifugal force upon reversal of the machine. To reduce such wear, many times this requires complete stoppage of the machine, waiting a time period, and then slowly beginning the reverse process. Alternatively, the reversal can be so violent as to damage or break the machine.
There is therefore a real need in the art to provide an improved reversing weight assembly for a vibratory bowl finishing machine which improves over or solves the problems and deficiencies in the art.
Another object of the present invention is to provide an assembly as above described which automatically allows for reversal of the top weight of the machine, yet allows quick and easy adjustment of the offset or trailing angle in either direction for the top weight as compared to the bottom weight.
A still further object of the present invention is to provide an assembly as above described which presents dampening of the automatic transfer of the position of the top weight upon reversal of the machine.
A further object of the present invention is to provide an assembly as above described which is economical, efficient, and durable.
These and other objects, features and advantages of the present invention will become more apparent with reference to the accompanying specification and claims.